Return to stock Help!!!

Hey fellas. I bought a m9 earlier today. It was rooted and had twrp. Anyways I tried upgrading and it went into recovery. Me being the idiot I am, I erased and wiped everything. Now there is NO OS installed. All I'm trying to do it get back to stock. This is my first HTC and I am very confused. I don't really want it rooted anymore. Just stock OS.

Can anyone point me to a tutorial or give me the necessary steps to take to get back to stock?

It is a tmobile m9. Thanks in advance.